From an interview with Milton Friedman (2), a good story about Mises and the Mont Pelerin Society. It's told to critique him; but to me, it shows Mises's integrity and principles.
INTERVIEWER: Some of those debates became very, very heated. I think [Ludwig] von Mises once stormed out.
MILTON FRIEDMAN: Oh, yes, he did. Yes, in the middle of a debate on the subject of distribution of income, in which you had people who you would hardly call socialist or egalitarian — people like Lionel Robbins, like George Stigler, like Frank Knight, like myself — Mises got up and said, "You're all a bunch of socialists," and walked right out of the room. (laughs) But Mises was a person of very strong views and rather intolerant about any differences of opinion.